This system forms part of Bolton's storage and overflow facilities with 2 CSO chambers and a 10000m³ tank.

Diocletian built the largest of the public baths in Rome, with room for thousands of bathers. I met with Snake Oil and Viraleye one evening to pop some lids and see if we could see something of the beast.

A large split CSO chamber takes the flows from two sewers, each side with a non-screened weir. The overflow leaves the chamber via a grilled pipe, this limits the flow rate out of the chamber and large banks of mud had gathered. The mud had a fledgling eco-system developing as an army of worms munched through, supporting a small population of frogs and surprisingly newts.

One of the incoming sewers came from a further smaller CSO chamber upstream, this acts as as last ditch overflow for when the larger chamber backfills. The overflow culvert was 1.6m bolted segments which ran towards the river.

Just before the final stretch to the grilled Croal outfall was a chamber sporting a rectangular flap.

In-between the overflow from the large CSO and the flap was 10k cubic meters of offline tank.

The scale of the place was awesome but what struck me most was the absolute silence, despite that the air was pretty good.

Here's a crop of the last image featuring Snake Oil to show some scale.

A couple of dropshafts appeared to take the flow from the CSO down the tower into the tank, with an overflow lip straight over the side.

After a storm the pumping station above the tank empties the contents back into the main sewer, through a smallish pipe just downstream of the big CSO chamber. That must take quite a while.